Serum fluctuations of total and free tryptophan levels during the menstrual cycle are related to gonadotrophins and reflect brain serotonin utilization

BACKGROUND: Serotoninergic (5-HT) neurons are suggested to regulate estrous cycle in animal models. In the present study we evaluated whether a relationship exists between the serotoninergic precursors in the central nervous system and the gonadotrophin–ovarian cyclic function. METHODS: We measured 5-HT precursors [free (FT) and total (TT) tryptophan] and LH, FSH and 17β-estradiol (E2) levels in the serum of 15 fertile women with normal menstrual cycles during the follicular (cycle days 1–5, 7–11), mid-cycle (cycle days 14–16) and luteal (cycle days 17–19, 22–24) phases. RESULTS: TT and FT were significantly increased in the 7–11 and 17–19 cycle days and were decreased at mid-cycle (P